DISEASES. 593 



mg large numbers of horses, when the stables of mail and stage 

 coaches, and even those of military garrisons, were small, ill-venti- 

 lated and dirty, among horses standing in filth and soiled manure, 

 these afiections were relatively common ; with hygienic improve- 

 ments, they have almost disapj)eared. In the army, canker was 

 the cause of considerable annual loss, almost as serious as those 

 from glanders ; to-day it is rare and almost unknown. 



Improvements in the different breeds of horses, either by bet- 

 ter choice of reproducers, or by changes in the mode of feeding, 

 resulting from the progress of agricultural processes, the suppres- 

 sion of common pastures, etc., have contributed to render the 

 disease less common. 



Synqitoms. — It is seldom that the symptoms of canker can be 

 observed from the start ; slow in its progress, and not surexciting 

 the sensibHity of the parts, the disease may progress without 

 manifesting any ill effects, and consequently escape notice by the 

 owner or groom, nothing appearing to call his attention to the 

 affected foot. Thus, in a majority of cases canker is only dis- 

 covered after it has been in existence for a considerable period, 

 and when serious alterations have already taken place. It is 

 often at the shoeing shop, when the shoes are changed, that in 

 the laminse is observed a moisture more or less abundant, giving 

 rise to softening and raising of the hoof. The disease sometimes 

 attacks only one foot, often several feet at a time ; at times when 

 one foot is cured, another becomes affected, and the disease thus 

 appears traveling alternately from one foot to another. 



Usually the disease begins with the inflamation of the kerato- 

 genous membrane which covers, the median lacunae of the plantar 

 cushion ; the hoof covering this is softened, raised by a serOus 

 moisture, and once loose, is not renewed, the tissue producing it 

 having lost its function of secreting the horny substance, and now 

 secreting a serous element, which becomes the caseous matter of 

 which we shall speak hereafter. 



Sometimes the disease begins by moisture in the hollow of the 

 coronet, by a kind of grease, a disease which we shall see to be of 

 the same nature as canker. The is an oedematous swelling, warm, 

 somewhat painfvil, of the phalangeal region, first serous, then be- 

 coming opalescent, which seems to filtrate through the softened, 

 but not yet raised, epidermis. This inflammation, spreading little 

 by little toward the hoof, extends to the plantar keratogenous. 



